Phase II Trial of Combination of Bortezomib and Rituximab in Relapsed and/or Refractory Waldenstrom Macroglobulinemia: Preliminary Results.

INTRODUCTION: Previous studies have demonstrated the clinical activity of bortezomib as a single agent in patients with Waldenstrom Macroglobulinemia (WM). We performed preclinical studies that demonstrated synergistic activity of bortezomib with the anti-CD20 antibody rituximab in WM cell lines. This phase II study aimed to determine safety and activity of weekly bortezomib in combination with rituximab in patients with relapsed/refractory WM.

METHODS: Patients who had at least one previous therapy for WM, symptomatic, and who had relapsed or refractory disease were eligible. NCI CTCAE v3.0 was used for toxicity assessment. Response was assessed by criteria established at the second consensus panel for WM. All patients received bortezomib IV weekly at 1.6mg/m2 on days 1, 8, 15 q 28 days x 6 cycles and rituximab 375 mg/m2 at days 1, 8, 15, 22 on cycles 1 and 4.

RESULTS: 17 pts (10 men and 7 women, median age 62 years, range 43 – 81) have been treated to date. The median number of lines of prior treatment was 3 (range 1 – 5) including prior bortezomib and prior rituximab in some of those patients. The median IgM at baseline was 4070 mg/dL (range 1370– 10,800); median M-spike at baseline was 2.48 g/dL (range 1.5 – 4.87); and median hemoglobin was 11.0 g/dL (6.3–15.2). The median follow up was 5 months (range 1 – 11 months). Prior therapy included rituximab, nucleoside analogues (fludarabine and 2-CDA), combination chemotherapy (e.g CHOP, CVP), chlorambucil, and bortezomib. 13 pts are currently evaluable for response, best response to bortezomib and rituximab after 2 cycles are presented in Table 1. Median duration of response has not been reached. None of the patients progressed while on therapy with bortezomib and rituximab. Patients tolerated therapy well without significant toxicities: grade 3 peripheral neuropathy occurred in only 1 patient at cycle 6 and improved to grade 1 within 2 weeks of holding therapy. Other grade 3 and 4 toxicities included neutropenia in 3 patients, and anemia and hyponatremia in 1 patient. One patient discontinued therapy on study after 1 cycle because of inability to travel to study site and completed similar treatment off study and was unevaluable on this study. Attributable toxicities otherwise proved manageable with appropriate supportive care and the combination was generally well tolerated.

CONCLUSIONS: The combination of weekly bortezomib and rituximab has been well tolerated and demonstrates exciting activity achieving CR+ PR + MR in 85%, and/or stabilization of disease in 15% of evaluable patients with relapsed WM. No significant peripheral neuropathy was observed with this regimen. Updated data will be presented at the meeting.